Ultrarapid hardening cement compositions are produced by kneading ultrarapid hardening cement, water, fine aggregate, coarse aggregate, and the like. Such ultrarapid hardening cement compositions are excellent in rapid hardenability and capable of providing hardened products excellent in strength and durability. Therefore, such ultrarapid hardening cement compositions have been widely used in repair, reinforcement, or urgent construction of outer wall materials of buildings, building structures, or the like, and in production of concrete products. Such ultrarapid hardening cement compositions need to have enough initial fluidity and fluidity retention not to affect the work, and need to be excellent in strength and durability after hardened as well as in rapid hardenability. Further, such ultrarapid cement compositions need to exhibit these properties under low temperature atmosphere because such compositions are often used in winter when the hardening rate reduces.
In such ultrarapid hardening cement compositions, cement containing a calcium aluminate as a rapid hardening component (ultrarapid hardening cement) has been commonly used. It is known that the calcium aluminate as a rapid hardening component rapidly hydrates with kneading water to exhibit excellent initial strength. On the other hand, the rapid hydration of the calcium aluminate rapidly reduces the fluidity of the cement composition and complicates the kneading. Therefore, the workability needs to be improved by controlling such a hydration reaction and thereby improving the fluidity retention and the usable time sufficiently. The unit quantity of water contained in such a cement composition is reduced, and thereby performances of a hardened product of the composition are improved. Therefore, the workability needs to be improved without increase of the unit quantity of kneading water.
Various dispersants have been added to improve properties of the ultrarapid hardening cement composition, such as initial fluidity and usable time, or the unit quantity of water contained in the cement composition has been reduced to improve strength of the hardening product.
Cement dispersants containing, as a main component, a formaldehyde condensate of naphthalene sulfonate, a formaldehyde condensate of melamine sulfonate, or the like, and polycarboxylic acid cement dispersants have been known as dispersants contained in conventional ultrarapid hardening cement compositions.
However, such dispersants containing, as a main component, a formaldehyde condensate of naphthalene sulfonate, a formaldehyde condensate of melamine sulfonate, or the like, show limited cement dispersion effect or limited fluidity improvement effect if the dosage thereof exceeds a certain amount. Therefore, a cement dispersant capable of providing needed high fluidity, low unit quantity of water, initial fluidity, usable time, dispersibility, and the like, has been needed.
The compositions need to have sufficient fluidity during the work. However, such dispersants containing, as a main component, a formaldehyde condensate of naphthalene sulfonate, a formaldehyde condensate of melamine sulfonate, or the like, may be insufficient in usable time. It is known that a retarding agent needs to be added to the composition in order to maintain the fluidity attributed to the use of the dispersant during the work. However, the retarding agent may reduce the initial strength exhibiting property of the ultrarapid hardening cement composition if added too much, particularly under low temperature. Therefore, an ultrarapid hardening cement composition capable of maintaining the fluidity for the work even if containing a small amount of or not containing such a retarding agent, has been needed. These cement dispersants may contain residual formaldehyde used in the synthetic process. Therefore, an economically preferable ultrarapid hardening cement composition has been needed.
It is known that the polycarboxylic acid cement dispersants have dispersion effect higher than that of the cement dispersants containing, as a main component, a formaldehyde condensate of naphthalene sulfonate, a formaldehyde condensate of melamine sulfonate, and the like, generally. Such polycarboxylic acid cement dispersants exhibit excellent dispersibility if used to an ordinary portland cement. Therefore, the polycarboxylic acid admixtures show excellent dispersibility and can dramatically highly flow without changing the unit quantity of water, or can remarkably reduced the unit quantity of water while retaining a certain fluidity. For example, disclosed is a cement composition including a hydraulic material consisting essentially of calcium aluminates having 0.5 to 4.0 molar ratio of CaO/Al2O3 and a cement dispersing agent consisting essentially of a polycarboxylic acid-based polymer. In Example, a polycarboxylic acid cement dispersant is used (for example, referring to Japanese Kokai Publication No. Hei-11-217250 (pages 2 to 4)).
With respect to cases where a polycarboxylic acid cement dispersant is applied to an ultrarapid hardening cement composition, disclosed is a production method of a highly flowable rapid-hardening cement mix material having high flowability, comprising adding a polycarboxylic acid (salt) to paste, mortar or concrete, each of which has rapid hardening properties (for example, referring to Japanese Kokai Publication No. Hei-07-17749 (pages 1 and 2)). Also, disclosed is a powdery ultra-rapid-hardening cement composition containing an ultra-rapid hardening cement and a powdery polycarboxylic acid cement dispersant, and in Example, a polycarboxylic acid cement dispersant is used (for example, referring to Japanese Kokai Publication No. 2000-34159 (pages 1 and 2)). However, such cement compositions have room for improvement in order to not only have excellent rapid hardenability, high fluidity, low unit quantity of water, initial fluidity, usable time, dispersibility and the like, but also exhibit excellent initial strength under low temperature atmosphere and provide a hardened product with sufficiently excellent strength.